Power amplifier and radio wave transmitter having the same

ABSTRACT

A power amplifier ( 10 ) comprises: an A/D converter ( 11 ) for converting, to a time discrete signal, an envelope signal included in a high-frequency modulated signal and including only an amplitude modulated component of the high-frequency modulated signal; a switching amplifier ( 12 ) for amplifying the output signal of the A/D converter ( 11 ); a low-pass filter ( 13 ) for removing high frequency noise from the output signal of the switching amplifier ( 12 ); a plurality of high-frequency power amplifiers ( 15 - 1  to  15 - n ) for receiving the output signal of the low-pass filter ( 13 ) as a power supply and for amplifying a carrier signal included in the high-frequency modulated signal; and a power controller ( 14 ) for adjusting the average power of the output signal of the power amplifier ( 10 ) by controlling the total gains of the plurality of high-frequency power amplifiers ( 15 - 1  to  15 - n ).

TECHNICAL FIELD

The present invention relates to a power amplifier and a radio wavetransmitter having the same, and particularly, to a power amplifier anda radio wave transmitter having the same, which do not entail a changein SNR (Signal to Noise Ratio) of an output signal even if an averagepower of the output signal is changed.

BACKGROUND ART

In recent years, radio communications, such as those based on portabletelephones and the like, employ a modulation scheme which demonstrates ahigh frequency utilization efficiency and a large peak-to-average powerratio (PAPR).

In the field of radio communications, for amplifying a modulated signalincluding an amplitude modulated component using an AB-class amplifierwhich has been conventionally employed, sufficient back-off must betaken in order to maintain the linearity of an output signal. Generally,this back-off is required to be at least in the order of PAPR.

On the other hand, the AB-class amplifier exhibits a power efficiencywhich reaches a maximum at output saturation, and becomes lower as theback-off increases. As such, a modulated signal having larger PAPRencounters larger difficulties in increasing the power efficiency of apower amplifier.

A polar modulation type power amplifier is representative of a poweramplifier for highly efficiently amplifying such a modulated signalwhich has large PAPR. The polar modulation type power amplifieramplifies a high-frequency modulated signal for radio communications,which is generated on the basis of polar coordinate components ofamplitude and phase. Also, polar modulation type power amplifiersinclude one which is particularly referred to as an EER (EnvelopeElimination and Restoration) type power amplifier. The EER type poweramplifier is configured to substitute for an AB-class amplifier.

FIG. 1 shows the configuration of an RF (Radio Frequency) transmitter asan exemplary radio wave transmitter which comprises an associated polarmodulation type power amplifier.

The RF transmitter shown in FIG. 1 comprises digital baseband unit 201,analog baseband unit 205, and EER-type power amplifier 214.

Digital baseband unit 201 generates three types of signals, i.e., apower control signal, an I-signal, and a Q-signal which are delivered toanalog baseband unit 205 through power control signal output terminal202, I-signal output terminal 203, and Q-signal output terminal 204,respectively.

In analog baseband unit 205, the I-signal delivered from I-signal outputterminal 203 is applied to and converted to an analog signal by DA(Digital-to-Analog) converter 206. Likewise, the Q-signal delivered fromQ-signal output terminal 204 is applied to and converted to an analogsignal by DA converter 210.

The I-signal and Q-signal converted to analog signals are multiplied bysignals supplied from local oscillator 208 through phase shifter 209, bymixer 207 and mixer 211, respectively. In this event, the signalsupplied from phase shifter 209 to mixer 211 has a phase delayed by 90°from the signal supplied from phase shifter 209 to mixer 207.

The output signal of mixer 207 and the output signal of mixer 211 areadded by adder 212 to generate a high-frequency modulated signal. Thehigh-frequency modulated signal delivered from adder 212 is amplified byvariable gain amplifier 213, and then delivered to EER-type poweramplifier 214. In this event, the gain of variable gain amplifier 213 isvaried in accordance with a power control signal delivered from powercontrol signal output terminal 202.

In EER-type power amplifier 214, the high-frequency modulated signaldelivered from variable gain amplifier 213 is applied to envelopedetector 215 and limiter 219. Envelope detector 215 extracts an envelopesignal from the high frequency modulated signal input thereto. Theenvelope signal extracted by envelope detector 215 is linearly amplifiedin an amplification path which is provided with AD (Analog-to-Digital)converter 216, switching amplifier 217, and low-pass filter 218. Limiter219 extracts a phase modulated signal, which presents a substantiallyuniform envelope, from the high-frequency modulated signal inputthereto, and delivers the phase modulated signal to high-frequency poweramplifier 220. High-frequency power amplifier 220 is supplied with theenvelope signal delivered from low-pass filter 218 as a power supply,and amplifies the phase modulated signal delivered from limiter 219 bymultiplying the same by the power supply. The thus amplitude modulatedoutput signal is delivered from signal output terminal 221.

EER-type power amplifier 214 can increase the power efficiency becauseit can employ switching amplifier 217 which is highly efficient in theamplification of the envelope signal, and because the multiplicationprocessing can be highly efficiently performed in high-frequency poweramplifier 220.

A signal band handled by envelope detector 215 is similar to a signalband for the output signal of variable gain amplifier 213, and typicallyranges approximately from several hundreds of kHz to several tens ofMHz. Accordingly, the envelope signal can be amplified by a D-classamplifier or the like, which comprises AD converter 216 for generating abit stream signal such as PDM (Pulse Density Modulation) or the like,switching amplifier 217, and low-pass filter 218, ideally withoutcausing a power loss.

Meanwhile, high-frequency power amplifier 220 is operating in asaturation region with the output signal of low-pass filter 218 which isbeing supplied as a power supply. Generally, high-frequency poweramplifier 220 is characterized by operating at the highest powerefficiency when the output is saturated.

With the foregoing configuration, the power efficiency of EER-type poweramplifier 214 is given by the product of the power efficiency ofswitching amplifier 217 with the power efficiency of high-frequencypower amplifier 220, and theoretically, high-frequency power amplifier220 provides the highest efficiency at all times.

Alternatively, polar modulation type power amplifiers have been proposedfor performing amplitude modulation in different ways, other thanEER-type power amplifier 214 shown in FIG. 1. As an example, FIG. 2shows the configuration of a polar modulation type power amplifierdescribed in Patent Document 1.

The polar modulation type power amplifier shown in FIG. 2 performsamplitude modulation by switching the number of saturated amplificationunits 304 which are set to an operable state (is turned on) among aplurality of saturated amplification units 304.

First, local oscillator 303 applies a phase modulated signal to each ofthe plurality of saturated amplification units 304. On the other hand,an amplitude modulated signal is applied from modulated signal inputterminal 301, and is converted to a control signal for saturatedamplification units 304 by amplitude controller 306. The control signalfrom amplitude controller 306 determines whether each of a plurality ofsaturated amplification units 304, arranged in parallel, should be setinto an operable state or a sleep state (off-state). The phase modulatedsignals delivered from saturated amplification units 304 in the operablestate are combined by output combiner circuit 305, and delivered fromoutput terminal 302.

Here, the modulated signal delivered from output terminal 302 has anamplitude which is a sum total of the amplitudes of the phase modulatedsignals delivered from saturated amplification units 304. Accordingly,the amplitude modulation can be performed by varying the number ofsaturated amplification units 304 which are in the operable state.

However, since the polar modulation type power amplifiers shown in FIGS.1 and 2 convert an envelope signal to a time discrete signal which isquantified through AD conversion, quantization noise occurs. In thepolar modulation type amplifier, the quantization noise has a magnitudewhich is substantially uniform irrespective of output power, so that theoutput signal deteriorates in SNR particularly when the output powerdecreases more from a maximum power.

In the polar modulation type power amplifiers shown in FIGS. 1 and 2,the output signal varies in SNR depending on the output power for causeswhich are attributable to basic characteristics of the AD converter foruse in amplification of the envelope signal. FIG. 3 shows therelationship between an input power and SNR of an output signal in anideal AD converter.

As shown in FIG. 3, in an ideal AD converter, SNR (dB) of an outputsignal can be represented by a first-order function of input power (dBm)within the range of output saturation. This fact is shown, for example,in Non-Patent Document 1, Non-Patent Document 2, and the like.

For the reason set forth above, when an envelope signal applied to an ADconverter as an input signal has a lower average power, an envelopesignal delivered from the AD converter will deteriorate in SNR.

For example, in W-CDMA based communications, the radio wave strength isadjusted in accordance with the distance between a base station and aportable terminal. Accordingly, a W-CDMA based radio wave transmitterrequires a circuit for controlling the output power of a polarmodulation type power amplifier.

In the radio wave transmitter shown in FIG. 1, the output power ofEER-type power amplifier 214 is adjusted by variable gain amplifier 213which is positioned antecedent to AD converter 216. Consequently, sinceAD converter 216 is applied with an envelope signal with a varyingaverage power, SNR will vary in the envelope signal amplification path.

Likewise, SNR also varies in the polar modulation type power amplifiershown in FIG. 2. For controlling the output power with the polarmodulation type power amplifier shown in FIG. 2, it is necessary to varythe number of saturated amplification units 304 which are controlled tobe in operable state by amplitude controller 306. Amplitude controller306 plays the same role as AD converter 206 shown in FIG. 1, and thenumber of bits representative of the magnitude of an envelope signal isrepresented by the number of saturated amplification units 304 which arein operable state. Accordingly, the relationship between the input powerof the envelope signal and the SNR in the polar modulation type poweramplifier shown in FIG. 2 is the same as that shown in FIG. 3, so thatthe envelope signal varies in SNR due to variations in average power ofthe output signal.

As described above, in a power amplifier used in a radio wavetransmitter, a change in the average power of an output signal causesthe SNR to vary on an envelope signal amplification path, resulting invariations in SNR of the output signal. Particularly, the output signaltends to deteriorate in SNR when a power amplifier generates an outputsignal with reduced average power.

From the foregoing, the power amplifier has a challenge in maintainingSNR of the output signal substantially constant irrespective of theaverage power of the output signal.

Patent Document 1: JP2005-86673A (FIG. 4).

Non-Patent Document 1: “Systematic Design of Sigma-DeltaAnalog-to-Digital Converters,” authored by Ovidiu Bajdechi and Johan H.Huijsing, Kluwer Academic Publishers, p.16, FIG. 2.6.

Non-Patent Document 2: “Bandpass Sigma Delta Modulators,” authored byJurgen van Engelen and Rudy van de Plassche, Kluwer Academic Publishers,p.47, FIG. 4.7.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a poweramplifier and a radio wave transmitter having the same, which solve theproblems described above.

A power amplifier of the present invention is provided for amplifying ahigh-frequency modulated signal. The power amplifier is characterized bycomprising:

an AD converter for converting an envelope signal included in thehigh-frequency modulated signal, to a time discrete signal, where theenvelope signal includes only an amplitude modulated component of thehigh-frequency modulated signal;

a switching amplifier for amplifying an output signal of the ADconverter;

a low-pass filter for removing high-frequency noise from an outputsignal of the switching amplifier;

a plurality of high-frequency power amplifiers supplied with an outputsignal of the low-pass filter as a power supply for amplifying a carriersignal included in the high-frequency modulated signal; and

a power controller for controlling a total gain of the plurality ofhigh-frequency power amplifiers, thereby adjusting an average power ofan output signal of the power amplifier.

A first radio wave transmitter of the present invention is characterizedby further comprising:

the power amplifier;

a digital baseband circuit for generating a power control signal, anI-signal, and a Q-signal; and

a polar coordinate conversion circuit for generating the envelope signaland the carrier signal based on the I-signal and the Q-signal deliveredfrom the digital baseband circuit,

wherein the AD converter receives the envelope signal delivered from thepolar coordinate conversion circuit,

the plurality of high-frequency power amplifiers receive the carriersignal delivered from the polar coordinate conversion circuit, and

the power controller receives the power control signal delivered fromthe digital baseband circuit, and conducts on/off control for theplurality of high-frequency power amplifiers based on the power controlsignal to adjust the average power of the output signal of the poweramplifier.

A second radio wave transmitter of the present invention ischaracterized by further comprising:

the power amplifier;

a digital baseband circuit for generating a power control signal, anI-signal, and a Q-signal; and

a polar coordinate conversion circuit for generating the high-frequencymodulated signal based on the I-signal and the Q-signal delivered fromthe digital baseband circuit, and further generating the envelope signaland the carrier signal based on the high-frequency modulated signal,

wherein the AD converter receives the envelope signal delivered from thepolar coordinate conversion circuit,

a high-frequency power amplifier at a first stage among the plurality ofhigh-frequency power amplifiers receives the carrier signal deliveredfrom the polar coordinate conversion circuit, and

the power controller receives the power control signal delivered fromthe digital baseband circuit, and conducts switching control for thehigh frequency switches based on the power control signal to adjust theaverage power of the output signal of the power amplifier.

In the power amplifier of the present invention, the envelope signal isamplified by the AD converter, switching amplifier, and low pass filter,while the average power of the output signals of the power amplifiers isadjusted by the power controller, and the plurality of high-frequencypower amplifiers.

In particular, in the power amplifier of the present invention, sincethe amplification of the envelope signal is performed independently ofthe adjustments to the average power of the output signals, the averagepower of the output signals is not adjusted antecedent to the ADconverter which is located on an envelope signal amplification path.

Accordingly, the average power of the envelope signal, applied to the ADconverter as an input signal, does not vary depending on the averagepower of the output signals, and remains substantially constant.

As a result, since the output signal of the AD converter presents asubstantially constant SNR at all times, the power amplifier cangenerate an output signal with a substantially constant SNR at alltimes.

For the reasons set forth above, the power amplifier can advantageouslymaintain the SNR of its output signal substantially constant at alltimes independently of the average power of the output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1]

A diagram showing the configuration of a radio wave transmitter whichcomprises an associated EER-type power amplifier.

[FIG. 2]

A diagram showing the configuration of an associated polar modulationtype power amplifier.

[FIG. 3]

A diagram for describing the SNR characteristic of an AD converter.

[FIG. 4]

A diagram showing the configuration of a power amplifier according to afirst embodiment of the present invention.

[FIG. 5]

A diagram for describing the relationship between output power andlinearity in the power amplifier according to the first embodiment ofthe present invention.

[FIG. 6]

A diagram showing the configuration of a radio wave transmitter whichcomprises a power amplifier according to a second embodiment of thepresent invention.

[FIG. 7]

A diagram showing the configuration of a radio wave transmitter whichcomprises a power amplifier according to a third embodiment of thepresent invention.

[FIG. 8]

A diagram for describing a method of controlling output power in poweramplifiers according to a third and a fifth embodiment of the presentinvention.

[FIG. 9]

A diagram for describing the relationship between the output power andlinearity in the power amplifiers according to the third and fifthembodiments of the present invention.

[FIG. 10]

A diagram showing the configuration of a radio wave transmitter whichcomprises a power amplifier according to a fourth embodiment of thepresent invention.

[FIG. 11]

A diagram showing the configuration of a radio wave transmitter whichcomprises the power amplifier according to the fifth embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the best mode for carrying out the present inventionwill be described with reference to the drawings.

Notably, while the following description will be given on the assumptionthat a power amplifier according to the present invention is a polarmodulation type power amplifier, the present invention is not so limitedbut can be applied to an envelope tracking type power amplifier whichperforms an operation referred to as “envelope tracking.” In thisrespect, a description will be given later.

First Embodiment

FIG. 4 shows the configuration of power amplifier 10 according to afirst embodiment of the present invention.

As shown in FIG. 4, power amplifier 10 of this embodiment comprises ADconverter 11, switching amplifier 12, low-pass filter 13, powercontroller 14, a plurality of high-frequency power amplifiers 15-1˜15-n(n is an integer given by n≧2), and modulated signal output terminal 16.

AD converter 11 is applied with an envelope signal which includes onlyan amplitude modulated component of a high-frequency modulated signalfor use in radio communications for conversion of the same to a timediscrete signal.

Switching amplifier 12 amplifies the output signal of AD converter 11.

Low-pass filter 13 removes high-frequency noise from the output signalof switching amplifier 12.

Each of the plurality of high-frequency power amplifiers 15-1˜15-n aresupplied with the output signal of low-pass filter 13 as a power supply,and used for amplifying a carrier signal included in the high-frequencymodulated signal. While the plurality of high-frequency power amplifiers15-1˜15-n are arranged in parallel in FIG. 4, they can be alternativelyarranged in series.

Power controller 14 controls a total gain of the plurality ofhigh-frequency power amplifiers 15-1˜15-n to adjust the average power ofthe output signal of power amplifier 10. The output signal (modulatedsignal) whose average power has been adjusted by power controller 14, isdelivered from modulated signal output terminal 16.

In power amplifier 10 of this embodiment, an envelope signal isamplified by AD converter 11, switching amplifier 12, and low-passfilter 13. Specifically, AD converter 11 converts an envelope signalincluded in a high-frequency modulated signal to a time discrete signal,switching amplifier 12 amplifies the output signal of AD converter 11,and low-pass filter 13 removes high-frequency noise from the outputsignal of switching amplifier 12. The output signal of low-pass filter13 is supplied to the plurality of high-frequency power amplifiers15-1˜15-n as a power supply.

On the other hand, the average power of the output signal of poweramplifier 10 is adjusted by power controller 14 and a plurality ofhigh-frequency power amplifiers 15-1˜15-n. Specifically, the carriersignal included in the high-frequency modulated signal is amplifiedusing the plurality of high-frequency power amplifiers 15-1˜15-n whichare supplied with the output signal of low-pass filter 13 as a powersupply. In this event, power controller 14 controls the total gain ofthe plurality of high-frequency power amplifiers 15-1˜15-n to adjust theaverage power of the output signal of power amplifier 10.

Stated another way, power amplifier 10 of this embodiment amplifies theenvelope signal and adjusts the average power of the output signal,independently of each other.

As such, even when the average power of the output signal of poweramplifier 10 is adjusted, for example, for adjusting the radio wavestrength in W-CDMA based communication, the average power of the outputsignal is not adjusted antecedent to AD converter 11 which is includedin the envelope signal amplification path.

Consequently, the average power of the envelope signal applied to ADconverter 11 as an input signal does not vary depending on the averagepower of the output signal, and is substantially constant at all times.

As a result, since the output signal of AD converter 11 presents asubstantially constant SNR at all times, the SNR of the output signal ofAD converter 11 can be maintained substantially constant.

FIG. 5 shows the relationship between the average power of the outputsignal and ACPR (Adjacent Channel Power Ratio) of the output signal inpower amplifier 10 of this embodiment.

In the polar modulation type power amplifiers shown in FIGS. 1 and 2,ACPR of the output signal increases as the average power of the outputsignal is reduced. This is caused by the fact that when an attempt ismade to reduce the average power of the output signal, this reductionentails a need for reducing the average power of the input signal to theAD converter, which results in a reduction in SNR of the output signalof the AD converter.

In contrast, in power amplifier 10 of this embodiment, the average powerof the output signal is adjusted by power controller 14 and theplurality of high-frequency power amplifiers 15-1˜15-n, which arelocated on a path independent of the envelope signal amplification pathwhich includes AD converter 11, so that AD converter 11 is applied withan input signal which has a substantially constant average power, thusmaking ACPR of the output signal substantially constant at all times.

Second Embodiment

FIG. 6 shows the configuration of a radio wave transmitter whichcomprises power amplifier 110 according to a second embodiment of thepresent invention.

The radio wave transmitter shown in FIG. 6 comprises digital basebandunit 101, polar coordinate conversion circuit 105, and power amplifier110.

Digital baseband unit 101 in turn comprises power control signal outputterminal 102, I-signal output terminal 103, and Q-signal output terminal104. Polar coordinate conversion circuit 105 in turn comprises I-signalinput terminal 106, Q-signal input terminal 107, envelope signal outputterminal 108, and phase modulated signal output terminal 109. Poweramplifier 110 in turn comprises AD converter 111, switching amplifier112, low-pass filter 113, power controller 114, high-frequency poweramplifiers 115-1˜115-n (n is an integer given by n≧2), power combinercircuit 116, and modulated signal output terminal 117.

Digital baseband unit 101 generates a power control signal, an I-signal,and a Q-signal. The power control signal is delivered from power controlsignal output terminal 102 to power amplifier 110. On the other hand,the I-signal and Q-signal are delivered to polar coordinate conversioncircuit 105 from I-signal output terminal 103 and Q-signal outputterminal 104, respectively.

Polar coordinate conversion circuit 105 is applied with the I-signal andQ-signal from I-signal input terminal 106 and Q-signal input terminal107, respectively. Polar coordinate conversion circuit 105 generates ahigh-frequency modulated signal based on the I/Q signals appliedthereto. Further, polar coordinate conversion circuit 105 generates anenvelope signal which includes only an amplitude modulated component ofthe high-frequency modulated signal, and also generates a phasemodulated signal as a carrier signal. The phase modulated signalincludes only a phase modulated component of the high-frequencymodulated signal, is up-converted to a carrier frequency band, andpresents a substantially constant envelope. The envelope signal andphase modulated signal are respectively delivered from envelope signaloutput terminal 108 and phase modulated signal output terminal 109 topower amplifier 110.

In power amplifier 110, the envelope signal delivered from envelopesignal output terminal 108 is applied to AD converter 111. The powercontrol signal delivered from power control signal output terminal 102in turn is applied to power controller 114. Further, the phase modulatedsignal delivered from phase modulated signal output terminal 109 isapplied to high-frequency power amplifiers 115-1˜115-n. The envelopesignal applied to AD converter 111 has a substantially constant averagepower at all times. This is because the output power of power amplifier110 is not controlled antecedent to AD converter 111, but is controlledby way of a path different from the envelope signal amplification path.In contrast, in EER-type power amplifier 214 shown in FIG. 1, since theoutput power of EER-type power amplifier 214 is controlled by variablegain amplifier 213 antecedent to AD converter 216, the average power ofthe envelope signal applied to AD converter 216 varies. For a similarreason, the average power of the phase modulated signal applied tohigh-frequency power amplifiers 115-1˜115-n is also substantiallyconstant at all times.

AD converter 111 converts the envelope signal delivered from envelopesignal output terminal 108 to a time discrete signal which is deliveredto switching amplifier 112.

Switching amplifier 112 highly efficiently amplifies the time discretesignal applied thereto, and delivers the amplified time discrete signalto power supply terminals of high-frequency power amplifiers 115-1˜115-nthrough low-pass filter 113 to remove high-frequency noise.

Power controller 114 individually generates control signals delivered tothe plurality of high-frequency power amplifiers 115-1˜115-n based onthe power control signal delivered from power control signal outputterminal 102.

The control signal delivered from power controller 114 determines thateach of high-frequency power amplifiers 115-1˜115-n is to enter anon-state or an off-state. High-frequency power amplifier 115-1˜115-n,when in on-state, amplifies the phase modulated signal delivered fromphase modulated signal output terminal 109 by multiplying the same bythe envelope signal delivered from low-pass filter 113 for use as apower supply, to generate a modulated signal. On the other hand,high-frequency power amplifier 115-1˜115-n, when in the off-state, doesnot generate a modulated signal, but remains in a sleep state. Outputsignals of high-frequency power amplifiers 115-1˜115-n are combined bypower combiner circuit 116, and delivered from modulated signal outputterminal 117.

The I/Q signals and the modulated signal generated from the I/Q signalsare signals which contain communication data. On the contrary, the powercontrol signal is a signal for varying the average power of the outputsignal of power amplifier 110 in accordance with the distance betweencommunication devices (for example, between a portable terminal and abase station when the portable terminal is a portable telephone).

Power amplifier 110 of this embodiment adjusts the average power of theoutput signal in terms of total output power of high-frequency poweramplifiers 115-1˜115-n which are in the on-state. In this way, ADconverter 111 used to amplify an envelope signal is applied at all timeswith an envelope signal having a substantially constant average powerbecause the average power of the output signal is not adjustedantecedent thereto. Accordingly, the envelope signal is converted to atime discrete signal with a substantially constant SNR by AD converter111.

Since AD converter 111 is a main noise source in power amplifier 110 ofthis embodiment, if the output signal of AD converter 111 presents asubstantially constant SNR at all times, the modulated signal deliveredfrom modulated signal output terminal 117 also presents a substantiallyconstant SNR.

Notably, in power amplifier 110 of this embodiment, a method ofdesigning/controlling high-frequency power amplifiers 115-1˜115-n can bemodified in accordance with a desired output power.

For example, when all high-frequency power amplifiers 115-1˜115-n aredesigned such that their saturated output powers are equal to oneanother, a proportional relationship is developed between the number ofhigh-frequency power amplifiers 115-1˜115-n in the on-state and theoutput power, thus making it easier to control the output power. In thisevent, power controller 114 converts the power control signal deliveredfrom power control signal output terminal 102 to a value at one of (n+1)steps from zero to n, and controls high-frequency power amplifiers115-1˜115-n such that the converted value at one of (n+1) steps is equalto the number of high-frequency power amplifiers 115-1˜115-n which areturned on.

As another example, it is also contemplated to design high-frequencypower amplifiers 115-1˜115-n such that their saturated output powers arerespectively provided in the ratio of, such as 1:2:4: . . . :2(n−1). Indoing so, the output power can be controlled in a range of zero to2(n−1) times as large as the minimum step width of the output power.Here, the minimum step width of the output power is equal to thesaturated power of high-frequency power amplifier 115-1. In this event,power controller 114 converts the power control signal delivered frompower control signal output terminal 102 to an n-bit signal, andcontrols high-frequency power amplifiers 115-1˜115-n such thathigh-frequency power amplifier 115-k is brought into the on-state when ak-th bit (1≦k≦n) counted from the least significant bit is “1” (High),and is brought into off-state when the k-th bit is “0” (Low).

Alternatively, in power amplifier 110 of this embodiment, the phasemodulated signal delivered from phase modulated signal output terminal109 may be replaced with a modulated signal which includes a phasemodulated component and an amplitude modulated component of ahigh-frequency modulated signal. In this configuration, power amplifier110 performs an operation referred to as “envelope tracking,” andbehaves as an envelope tracking type power amplifier.

Third Embodiment

A power amplifier according to a third embodiment of the presentinvention is modified such that the average power of the output signalcan be adjusted by a method other than the on/off control ofhigh-frequency power amplifiers 115-1˜115-n, as performed in the secondembodiment.

FIG. 7 shows the configuration of a radio wave transmitter whichcomprises power amplifier 410 according to the third embodiment of thepresent invention.

The radio wave transmitter shown in FIG. 7 comprises digital basebandunit 401, polar coordinate conversion circuit 405, and power amplifier410, as is the case with the second embodiment.

Digital baseband unit 401 in turn comprises power control signal outputterminal 402, I-signal output terminal 403, and Q-signal output terminal404. Polar coordinate conversion circuit 405 in turn comprises I-signalinput terminal 406, Q-signal input terminal 407, envelope signal outputterminal 408, and phase modulated signal output terminal 409. Poweramplifier 410 in turn comprises variable gain amplifier 418, ADconverter 411, switching amplifier 412, low-pass filter 413, powercontroller 414, high-frequency variable gain amplifier 419,high-frequency power amplifiers 415-1˜415-n (n is an integer given byn≧2), power combiner circuit 416, and modulated signal output terminal417.

Digital baseband unit 401 generates a power control signal, an I-signal,and a Q-signal. The power control signal is delivered from power controlsignal output terminal 402 to power amplifier 401. The I-signal andQ-signal are delivered to polar coordinate conversion circuit 405 fromI-signal output terminal 403 and Q-signal output terminal 404,respectively.

Polar coordinate conversion circuit 405 is applied with the I-signal andQ-signal from I-signal input terminal 406 and Q-signal input terminal407, respectively. Polar coordinate conversion circuit 405 generates ahigh-frequency modulated signal based on the I/Q signals appliedthereto. Further, polar coordinate conversion circuit 405 generates anenvelope signal which includes only an amplitude modulated component ofthe high-frequency modulated signal, and also generates a phasemodulated signal as a carrier signal. The phase modulated signalincludes only a phase modulated component of the high-frequencymodulated signal, is up-converted to a carrier frequency band, andpresents a substantially constant envelope. The envelope signal andphase modulated signal are respectively delivered from envelope signaloutput terminal 408 and phase modulated signal output terminal 409 topower amplifier 410.

In power amplifier 410, the envelope signal delivered from envelopesignal output terminal 408 is applied to variable gain amplifier 418.The power control signal delivered from power control signal outputterminal 402 in turn is applied to power controller 414. The phasemodulated signal delivered from phase modulated signal output terminal409 in turn is delivered to high-frequency variable gain amplifier 419.

Variable gain amplifier 418 is positioned antecedent to AD converter411. Variable gain amplifier 418, whose gain is controlled by powercontroller 414, delivers a power-adjusted envelope signal to ADconverter 411.

High-frequency variable gain amplifier 419 is positioned antecedent tohigh-frequency power amplifiers 415-1˜415-n. Likewise, high-frequencyvariable gain amplifier 419, whose gain is controlled by powercontroller 414, delivers a power-adjusted phase modulated signal tohigh-frequency power amplifiers 415-1˜415-n.

AD converter 411 converts the envelope signal delivered from variablegain amplifier 418 to a time discrete signal which is delivered toswitching amplifier 412.

Switching amplifier 412 highly efficiently amplifies the time discretesignal applied thereto, and delivers the amplified time discrete signalto power supply terminals of high-frequency power amplifiers 415-1˜415-nthrough low-pass filter 413 to remove high-frequency noise.

Power controller 414 individually generates control signals delivered tovariable gain amplifier 418, high-frequency variable gain amplifier 419,and the plurality of high-frequency power amplifiers 415-1˜415-n basedon the power control signal delivered from power control signal outputterminal 402.

The control signal delivered from power controller 414 determines thateach of high-frequency power amplifiers 415-1˜415-n is to enter anon-state or an off-state. High-frequency power amplifier 415-1˜415-n,when in the on-state, amplifies the phase modulated signal deliveredfrom high-frequency variable gain amplifier 419 by multiplying the sameby the envelope signal delivered from low-pass filter 413 for use as apower supply, to generate a modulated signal. On the other hand,high-frequency power amplifier 415-1˜415-n, when in the off-state, doesnot generate the modulated signal, but remains in a sleep state. Outputsignals of high-frequency power amplifiers 415-1˜415-n are combined bypower combiner circuit 416, and delivered from modulated signal outputterminal 417.

Power amplifier 410 of this embodiment comprises variable gain amplifier418 and high-frequency gain amplifier 419 added to the configuration ofthe second embodiment and is modified such that the average power of theoutput signal can be adjusted by a method other than the on/off controlof high-frequency power amplifiers 415-1˜415-n. With this modification,the average power of the output signal can be adjusted with sufficientaccuracy, while the linearity is not largely damaged, even if a reducednumber of high-frequency power amplifiers 415-1˜415-n are turned on.

FIG. 8 shows the relationship between the input power of AD converter411 and the output power at modulated signal output terminal 417 inpower amplifier 410 of this embodiment.

As shown in FIG. 8, in power amplifier 410 of this embodiment,high-frequency power amplifiers 415-1˜415-n are turned on/off when theoutput power is largely changed, and fine adjustments of the outputpower are made by varying the gain of variable gain amplifier 418. Byconducting the power control as shown in FIG. 8, variations in inputpower of AD converter 411 can be limited to a smaller range, as comparedwith variations in output power of modulated signal output terminal 417.AD converter 411 provides an output signal with a higher SNR since theinput power is larger (see FIG. 3). Accordingly, the linearity (ACPR) ofthe modulated signal delivered from modulated signal output terminal 417behaves as shown in FIG. 9 in accordance with the magnitude of theoutput power.

Notably, in power amplifier 410 of this embodiment, a method ofdesigning/controlling high-frequency power amplifiers 415-1˜415-n can bemodified in accordance with a desired output power.

For example, when all high-frequency power amplifiers 415-1˜415-n aredesigned such that their saturated output powers are equal to oneanother, a proportional relationship is developed between the number ofhigh-frequency power amplifiers 415-1˜415-n in the on-state and theoutput power, thus making it easier to control the output power. In thisevent, power controller 414 converts the power control signal deliveredfrom power control signal output terminal 402 to a value at one of (n+1)steps from zero to n, and controls high-frequency power amplifiers415-1˜415-n such that the converted value at one of (n+1) steps is equalto the number of high-frequency power amplifiers 415-1˜415-n which areturned on.

As another example, it is also contemplated to design high-frequencypower amplifiers 415-1˜415-n such that their saturated output powers arerespectively provided in the ratio of, such as 1:2:4: . . . :2(n−1). Indoing so, the output power can be controlled in a range of zero to2(n−1) times as large as a minimum step width of the output power. Here,the minimum step width of the output power is equal to the saturatedpower of high-frequency power amplifier 415-1. In this event, powercontroller 414 converts the power control signal delivered from powercontrol signal output terminal 402 to an n-bit signal, and controlshigh-frequency power amplifiers 415-1˜415-n such that high-frequencypower amplifier 415-k is brought into on-state when a k-th bit (1≦k≦n)counted from the least significant bit is “1” (High), and is broughtinto off-state when it is zero (Low).

High-frequency variable gain amplifier 419 serves to allowhigh-frequency power amplifiers 415-1˜415-n to operate in an optimallysaturated state. High-frequency power amplifiers 415-1˜415-nalternatively enter a saturated state or a sleep state, where thelinearity and efficiency vary in response to variations in averagevoltage of the power supply provided from low-pass filter 413. Suchvariations in linearity and efficiency can be corrected for by adjustingthe average input power of high-frequency power amplifiers 415-1˜415-nby high-frequency variable gain amplifier 419. However, no problem willarise as long as sufficient power is ensured to saturate high-frequencypower amplifiers 415-1˜415-n. Accordingly, high-frequency variable gainamplifier 419 is not an essential component for this embodiment, and canbe omitted if phase modulated signal output terminal 409 is directlycoupled to high-frequency power amplifiers 415-1˜415-n.

Alternatively, in power amplifier 410 of this embodiment, the phasemodulated signal delivered from phase modulated signal output terminal409 may be replaced with a modulated signal which includes a phasemodulated component and an amplitude modulated component of ahigh-frequency modulated signal. In this configuration, power amplifier410 performs an operation referred to as “envelope tracking,” andbehaves as an envelope tracking type power amplifier.

Fourth Embodiment

FIG. 10 shows the configuration of a radio wave transmitter whichcomprises power amplifier 510 according to a fourth embodiment of thepresent invention.

The radio wave transmitter shown in FIG. 10 comprises digital basebandunit 501, polar coordinate conversion circuit 505, and power amplifier510, as is the case with the second and third embodiments.

Digital baseband unit 501 in turn comprises power control signal outputterminal 502, I-signal output terminal 503, and Q-signal output terminal504. Polar coordinate conversion circuit 505 in turn comprises I-signalinput terminal 506, Q-signal input terminal 507, envelope signal outputterminal 508, and phase modulated signal output terminal 509. Poweramplifier 510 in turn comprises AD converter 511, switching amplifier512, low-pass filter 513, power controller 514, high-frequency powerpre-amplifier 515, high-frequency switches 516-1˜516-n (integer given byn≧1), high-frequency power amplifiers 517-1˜517-n (integer given byn≧2), matching circuits 518-1˜518-n (integer given by n≧1), andmodulated signal output terminal 519. Notably, in this embodiment, poweramplifier 510 comprises a plurality (n+1) of high-frequency poweramplifiers, where a high-frequency power amplifier at the first stage isparticularly designated by high-frequency power pre-amplifier 515, andthe remaining ones are designated by high-frequency power amplifiers517-1˜517-n.

Digital baseband unit 501 generates a power control signal, an I-signal,and a Q-signal. The power control signal is delivered from power controlsignal output terminal 502 to power amplifier 510. The I-signal andQ-signal are delivered to polar coordinate conversion circuit 505 fromI-signal output terminal 503 and Q-signal output terminal 504,respectively.

Polar coordinate conversion circuit 505 is applied with the I-signal andQ-signal from I-signal input terminal 506 and Q-signal input terminal507, respectively. Polar coordinate conversion circuit 505 generates ahigh-frequency modulated signal based on the I/Q signals appliedthereto. Further, polar coordinate conversion circuit 505 generates anenvelope signal which includes only an amplitude modulated component ofthe high-frequency modulated signal, and also generates a phasemodulated signal as a carrier signal. The phase modulated signalincludes only a phase modulated component of the high-frequencymodulated signal, is up-converted to a carrier frequency band, andpresents a substantially constant envelope. The envelope signal andphase modulated signal are respectively delivered from envelope signaloutput terminal 508 and phase modulated signal output terminal 509 topower amplifier 510.

In power amplifier 510, the envelope signal delivered from envelopesignal output terminal 508 is applied to AD converter 511. The powercontrol signal delivered from power control signal output terminal 502in turn is applied to power controller 514. The phase modulated signaldelivered from phase modulated signal output terminal 509 in turn isdelivered to high-frequency power pre-amplifier 515. The envelope signalapplied to AD converter 511 has substantially constant average power atall times. This is because the output power of power amplifier 510 isnot controlled antecedent to AD converter 511, but is controlled by wayof a path different from the envelope signal amplification path. For asimilar reason, the signal applied to high-frequency powerpre-amplifiers 515 also has a substantially constant average power atall times.

AD converter 511 converts the envelope signal delivered from envelopesignal output terminal 508 to a time discrete signal which is deliveredto switching amplifier 512.

Switching amplifier 512 highly efficiently amplifies the time discretesignal applied thereto, and delivers the amplified time discrete signalto power supplies of high-frequency power pre-amplifier 515 andhigh-frequency power amplifiers 517-1˜517-n through low-pass filter 513for removing high-frequency noise.

Power controller 514 individually generates control signals delivered tohigh-frequency switches 516-1˜516-n based on the power control signaldelivered from power control signal output terminal 502.

High-frequency power pre-amplifier 515 amplifies the phase modulatedsignal delivered from phase modulated signal output terminal 509 bymultiplying the same by the envelope signal delivered from low-passfilter 513 for use as a power supply, and delivers its output signal tofollowing high-frequency switch 516-1.

High-frequency switches 516-1˜516-n are one-input, two-output switcheswhich are respectively connected antecedent to high-frequency poweramplifiers 517-1˜517-n. High-frequency switch 516-1 has an inputterminal connected to high-frequency power pre-amplifier 515, and afirst output terminal connected to following high-frequency poweramplifier 517-1. High-frequency switch 516-k (2≦k≦n) has an inputterminal connected to preceding high-frequency power amplifier 517-o(o=k−1), and a first output terminal connected to followinghigh-frequency power amplifier 517-k. Additionally, high-frequencyswitches 516-k (1≦k≦n) have their respective second output terminalsconnected to matching circuit 518-k.

High-frequency power amplifier 517-k (1≦k≦n−1) amplifies the outputsignal of preceding high-frequency switch 516-k, and delivers its outputsignal to following high-frequency switch 516-m (m=k+1). High-frequencypower amplifier 517-n amplifies the output signal of precedinghigh-frequency switch 516-n, and delivers its output signal to modulatedsignal output terminal 519.

High-frequency switch 516-k (1≦k≦n−1) determines, in accordance with acontrol signal delivered from power controller 514, whether a phasemodulated signal delivered from high-frequency power pre-amplifier 515should be amplified by high-frequency power amplifier 517-k and sent tofollowing high-frequency switch 516-m (m=k+1) or whether the phasemodulated signal should be delivered from modulated signal outputterminal 519 through matching circuit 518-k. When high-frequencyswitches 516-k are all connected to high-frequency power amplifiers517-k, the phase modulated signal delivered from phase modulated signaloutput terminal 509 travels up to high-frequency switch 516-n. In thisevent, high-frequency switch 516-n determines, in accordance with acontrol signal delivered from power controller 514, whether a phasemodulated signal applied thereto should be amplified by high-frequencypower amplifier 517-n and delivered from following modulated signaloutput terminal 519 or whether the phase modulated signal should bedelivered from modulated signal output terminal 519 through matchingcircuit 518-n.

In power amplifier 510 of this embodiment, high-frequency poweramplifiers 517-1˜517-n are designed such that their saturated outputpowers increase at later stages.

For example, when high-frequency power amplifiers 517-1˜517-n aredesigned such that their saturated output powers are provided in a ratioof, such as 1:A:A² . . . :A^((n−1)), step widths of output power aresubstantially constant on a decibel scale, thus facilitating the powercontrol. Here, A is an arbitrary positive real number. In this event,power controller 514 converts a power control signal delivered frompower control signal output terminal 502 to a logarithmic value which isfurther converted to a value at one of (n+1) steps from zero to n. Whenthe value resulting from the conversion to the (n+1) steps is j−1(1≦j≦n), power controller 514 controls high-frequency switches516-1˜516-n such that the phase modulated signal is delivered frommodulated signal output terminal 519 through matching circuit 518-j.

Since the gain of overall power amplifier 510 is determined by to whichstages high-frequency power amplifiers 517-1˜517-n are used, the averagepower of the output signal can be adjusted by selecting high-frequencyswitches 516-1˜516-n. Also, like the second embodiment, since theaverage power of the envelope signal applied to AD converter 511 is asubstantially constant at all times, the modulated signal delivered frommodulated signal output terminal 519 presents a substantially constantSNR at all times.

Alternatively, in power amplifier 510 of this embodiment, the phasemodulated signal delivered from phase modulated signal output terminal509 may be replaced with a modulated signal which includes a phasemodulated component and an amplitude modulated component of ahigh-frequency modulated signal. In this event, high-frequency powerpre-amplifier 515 can be removed such that phase modulated outputterminal 509 is directly coupled to high-frequency switch 516-1. In thisconfiguration, power amplifier 510 performs an operation referred to as“envelope tracking,” and behaves as an envelope tracking type poweramplifier.

Fifth Embodiment

A power amplifier according to a fifth embodiment of the presentinvention is modified such that the average power of the output signalcan be adjusted by a method other than the switching control ofhigh-frequency switches 516-1˜516-n, as performed in the fourthembodiment.

FIG. 11 shows the configuration of a radio wave transmitter whichcomprises power amplifier 610 according to the fifth embodiment of thepresent invention.

The radio wave transmitter shown in FIG. 11 comprises digital basebandunit 601, polar coordinate conversion circuit 605, and power amplifier610, as is the case with the second through fourth embodiments.

Digital baseband unit 601 in turn comprises power control signal outputterminal 602, I-signal output terminal 603, and Q-signal output terminal604. Polar coordinate conversion circuit 605 in turn comprises I-signalinput terminal 606, Q-signal input terminal 607, envelope signal outputterminal 608, and phase modulated signal output terminal 609. Poweramplifier 610 comprises variable gain amplifier 620, AD converter 611,switching amplifier 612, low-pass filter 613, power controller 614,high-frequency variable gain amplifier 621, high-frequency powerpre-amplifier 615, high-frequency switches 616-1˜616-n (integer given byn≧1), high frequency power amplifiers 617-1˜617-n (integer n≧1),matching circuits 618-1˜618-n (integer given by n≧1), and modulatedsignal output terminal 619. Notably, in this embodiment, power amplifier610 comprises a plurality (n+1) of high-frequency power amplifiers,where a high-frequency power amplifier at the first stage isparticularly designated by high-frequency power pre-amplifier 615, andthe remaining ones are designated by high-frequency power amplifiers617-1˜617-n.

Digital baseband unit 601 generates a power control signal, an I-signal,and a Q-signal. The power control signal is delivered from power controlsignal output terminal 602 to power amplifier 610. The I-signal andQ-signal are delivered to polar coordinate conversion circuit 605 fromI-signal output terminal 603 and Q-signal output terminal 604,respectively.

Polar coordinate conversion circuit 605 is applied with the I-signal andQ-signal from I-signal input terminal 606 and Q-signal input terminal607, respectively. Polar coordinate conversion circuit 605 generates ahigh-frequency modulated signal based on the I/Q signals appliedthereto. Further, polar coordinate conversion circuit 605 generates anenvelope signal which includes only an amplitude modulated component ofthe high-frequency modulated signal, and also generates a phasemodulated signal as a carrier signal. The phase modulated signalincludes only a phase modulated component of the high-frequencymodulated signal, is up-converted to a carrier frequency band, andpresents a substantially constant envelope. The envelope signal andphase modulated signal are respectively delivered from envelope signaloutput terminal 608 and phase modulated signal output terminal 609 topower amplifier 610.

In power amplifier 610, the envelope signal delivered from envelopesignal output terminal 608 is applied to variable gain amplifier 620.The power control signal delivered from power control signal outputterminal 602 in turn is applied to power controller 614. The phasemodulated signal delivered from phase modulated signal output terminal609 in turn is delivered to high-frequency variable gain amplifier 621.

Variable gain amplifier 620 is positioned antecedent to AD converter611. Variable gain amplifier 620, whose gain is controlled by powercontroller 614, delivers a power-adjusted envelope signal to ADconverter 611.

High-frequency variable gain amplifier 621 is positioned antecedent tohigh-frequency power pre-amplifier 615. Likewise, high-frequencyvariable gain amplifier 621, whose gain is controlled by powercontroller 614, delivers a power-adjusted modulated signal tohigh-frequency power pre-amplifier 615.

AD converter 611 converts the envelope signal delivered from variablegain amplifier 620 to a time discrete signal which is delivered toswitching amplifier 612.

Switching amplifier 612 highly efficiently amplifies the time discretesignal applied thereto, and delivers the amplified time discrete signalto the power supply terminals of high-frequency power pre-amplifier 615and high-frequency power amplifiers 617-1˜617-n through low-pass filter613 to remove high-frequency noise.

Power controller 614 individually generates control signals delivered toa plurality of variable gain amplifiers 620, high-frequency variablegain amplifier 621, and high-frequency power amplifiers 616-1˜616-nbased on the power control signal delivered from power control signaloutput terminal 602.

High-frequency power pre-amplifier 615 amplifies the phase modulatedsignal delivered from high-frequency variable gain amplifier 621 bymultiplying the same by the envelope signal delivered from low-passfilter 613 for use as a power supply, and delivers the output signal tofollowing high-frequency switch 616-1.

High-frequency switches 616-1˜616-n are one-input, two-output switcheswhich are respectively connected antecedent to high-frequency poweramplifiers 617-1˜617-n. High-frequency switch 616-1 has an inputterminal connected to high-frequency power pre-amplifier 615, and afirst output terminal connected to following high-frequency poweramplifier 617-1. High-frequency switch 616-k (2≦k≦n) has an inputterminal connected to preceding high-frequency power amplifier 617-o(o=k−1), and a first output terminal connected to followinghigh-frequency power amplifier 517-k. Additionally, high-frequencyswitches 616-k (1≦k≦n) have their respective second output terminalsconnected to matching circuit 618-k.

High-frequency power amplifier 617-k (1≦k≦n−1) amplifies the outputsignal of preceding high-frequency switch 616-k, and delivers its outputsignal to following high-frequency switch 616-m (m=k+1). High-frequencypower amplifier 617-n amplifies the output signal of previoushigh-frequency switch 616-n, and delivers its output signal to modulatedsignal output terminal 619.

High-frequency switch 616-k (1≦k≦n−1) determines, in accordance with acontrol signal delivered from power controller 614, whether a phasemodulated signal delivered from high-frequency power pre-amplifier 615should be amplified by high-frequency power amplifier 617-k and sent tofollowing high-frequency switch 616-m (m=k+1) or whether it should bedelivered from modulated signal output terminal 619 through matchingcircuit 618-k. When high-frequency switches 616-k are all connected tohigh-frequency power amplifiers 617-k, the phase modulated signaldelivered from phase modulated signal output terminal 609 travels up tohigh-frequency switch 616-n. In this event, high-frequency switch 616-ndetermines, in accordance with a control signal delivered from powercontroller 614, whether a phase modulated signal applied thereto shouldbe amplified by high-frequency power amplifier 617-n and delivered fromfollowing modulated signal output terminal 619 or whether the phasemodulated signal should be delivered from modulated signal outputterminal 619 through matching circuit 618-n.

In power amplifier 610 of this embodiment, high-frequency poweramplifiers 617-1˜617-n are designed such that their saturated outputpowers increase at later stages.

For example, when high-frequency power amplifiers 617-1˜617-n aredesigned such that their saturated output powers are provided in a ratioof, such as 1:A:A² . . . :A^((n−1)), step widths of output power aresubstantially constant on a decibel scale, thus facilitating powercontrol. Here, A is an arbitrary positive real number. In this event,power controller 614 converts a power control signal delivered frompower control signal output terminal 602 to a logarithmic value which isfurther converted to a value at one of (n+1) steps from zero to n. Whenthe value resulting from the conversion to the (n+1) steps is j−1(1≦j≦n), power controller 614 controls high-frequency switches616-1˜616-n such that the phase modulated signal is delivered frommodulated signal output terminal 619 through matching circuit 618-j.

Since the gain of overall power amplifier 610 is determined by to whichstages high-frequency power amplifiers 617-1˜617-n are used, the averagepower of the output signal can be adjusted by selecting high-frequencyswitches 616-1˜616-n. Also, when the gain control is additionallyconducted using variable gain amplifier 620 as is the case with thethird embodiment, the relationship between the output power and thelinearity can be established as shown in FIG. 9.

High-frequency variable gain amplifier 621 is provided for operatinghigh-frequency power pre-amplifier 615 and high-frequency poweramplifiers 617-1˜617-n in an optimally saturated state. The linearityand efficiency of high-frequency power pre-amplifier 615 andhigh-frequency power amplifiers 617-1˜617-n vary in response tovariations in the average voltage of the power supply provided fromlow-pass filter 613. Such variations in linearity and efficiency can becorrected for by adjusting the average input power of high-frequencypower amplifiers 617-1˜617-n by high-frequency variable gain amplifier621. However, no problem will arise in regard to operations as long assufficient power is ensured to saturate high-frequency powerpre-amplifier 615. Accordingly, high-frequency variable gain amplifier621 is not an essential component for this embodiment, and can beomitted if phase modulated signal output terminal 609 is directlycoupled to high-frequency power pre-amplifier 615.

Alternatively, in power amplifier 610 of this embodiment, the phasemodulated signal delivered from phase modulated signal output terminal609 may be replaced with a modulated signal which includes a phasemodulated component and an amplitude modulated component of ahigh-frequency modulated signal. In this event, high-frequency powerpre-amplifier 615 can be removed such that phase modulated outputterminal 609 is directly coupled to high-frequency switch 616-1. In thisconfiguration, power amplifier 610 performs an operation referred to as“envelope tracking,” and behaves as an envelope tracking type poweramplifier.

While the present invention has been described above with reference tosome embodiments, the present invention is not limited to the foregoingembodiments. The present invention can be modified in configuration anddetails in various manners which can be understood by those skilled inthe art to be within the scope of the present invention.

This application claims the priority based on Japanese PatentApplication No. 2007-287282 filed Nov. 5, 2007, the disclosure of whichis incorporated herein by reference in its entirety.

1. A power amplifier for amplifying a high-frequency modulated signal,characterized by comprising: a first processing unit for amplifying anenvelope signal included in the high-frequency modulated signal, saidenvelope signal including only an amplitude modulated component of thehigh-frequency modulated signal; and a second processing unit foradjusting an average power of an output signal of said power amplifier,wherein said first processing unit includes: an AD converter forconverting the envelope signal to a time discrete signal; a switchingamplifier for amplifying an output signal of said AD converter; and alow-pass filter for removing high-frequency noise from an output signalof said switching amplifier, and said second processing unit includes: aplurality of high-frequency power amplifiers supplied with an outputsignal of said low-pass filter as a power supply for amplifying acarrier signal included in the high-frequency modulated signal; and apower controller for controlling a total gain of said plurality ofhigh-frequency power amplifiers based on a power control signalindependent of the high-frequency modulated signal to adjust an averagepower of an output signal of said power amplifier.
 2. The poweramplifier according to claim 1, characterized in that: said plurality ofhigh-frequency power amplifiers are arranged in parallel, each of saidplurality of high-frequency power amplifiers amplifies the carriersignal by multiplying the carrier signal by the power supply, said poweramplifier further comprises a power combiner circuit for combiningoutput signals of said plurality of high-frequency power amplifiers andfor delivering the combined output signal to the outside, and said powercontroller conducts on/off control for said plurality of high-frequencypower amplifiers to adjust an average power of the output signal of saidpower amplifier.
 3. The power amplifier according to claim 2, furthercomprising: a variable gain amplifier positioned antecedent to said ADconverter, wherein said power controller controls the gain of saidvariable gain amplifier.
 4. The power amplifier according to claim 2,further comprising: a high-frequency variable gain amplifier positionedantecedent to said plurality of high-frequency power amplifiers, whereinsaid power controller controls the gain of said high-frequency variablegain amplifier.
 5. The power amplifier according to claim 2, whereinsaid envelope signal applied to said AD converter has a substantiallyconstant average power.
 6. The power amplifier according to claim 2,wherein said carrier signal is a signal which includes only a phasemodulated component of the high-frequency modulated signal.
 7. The poweramplifier according to claim 2, wherein said carrier signal is a signalwhich includes a phase modulated component and an amplitude modulatedcomponent of the high-frequency modulated signal.
 8. The power amplifieraccording to claim 1, characterized in that: said plurality ofhigh-frequency power amplifiers are arranged in series, said poweramplifier further comprises: high-frequency switches each having oneinput terminal and two output terminals, disposed between respectiveones of said plurality of high-frequency power amplifiers, each saidhigh-frequency switch having the input terminal connected to saidhigh-frequency power amplifier preceding thereto, and a first outputterminal connected to said high-frequency power amplifier subsequentthereto; and a matching circuit connected to second output terminals ofsaid high-frequency switches for delivering an output signal to theoutside, said high-frequency power amplifier at the first stagemultiplies the carrier signal by the power supply for amplification, anddelivers the output signal to said high-frequency switch subsequentthereto, said high-frequency power amplifiers except for those at thefirst stage and the final stage amplify an output signal of saidhigh-frequency switch antecedent thereto, and deliver an output signalto said high-frequency switch subsequent thereto, said high-frequencypower amplifier at the final stage amplifies an output signal of saidhigh-frequency switch antecedent thereto and delivers the output signalto the outside, and said power controller conducts switching control forsaid high-frequency switches to adjust the average power of the outputsignal of said power amplifier.
 9. The power amplifier according toclaim 8, further comprising a variable gain amplifier positionedantecedent to said AD converter, wherein said power controller controlsthe gain of said variable gain amplifier.
 10. The power amplifieraccording to claim 8, further comprising a high-frequency variable gainamplifier positioned antecedent to said plurality of high-frequencypower amplifiers, wherein said power controller controls the gain ofsaid high-frequency variable gain amplifier.
 11. The power amplifieraccording to claim 8, wherein said envelope signal applied to said ADconverter has a substantially constant average power.
 12. The poweramplifier according to claim 8, wherein said carrier signal is a signalwhich includes only a phase modulated component of the high-frequencymodulated signal.
 13. The power amplifier according to claim 8, whereinsaid carrier signal is a signal which includes a phase modulatedcomponent and an amplitude modulated component of the high-frequencymodulated signal.
 14. A radio wave transmitter comprising a poweramplifier according to claim 2, characterized by further comprising: adigital baseband circuit for generating the power control signal, anI-signal, and a Q-signal; and a polar coordinate conversion circuit forgenerating the envelope signal and the carrier signal based on theI-signal and the Q-signal delivered from said digital baseband circuit,wherein said AD converter receives the envelope signal delivered fromsaid polar coordinate conversion circuit, said plurality ofhigh-frequency power amplifiers receive the carrier signal deliveredfrom said polar coordinate conversion circuit, and said power controllerreceives the power control signal delivered from said digital basebandcircuit, and conducts on/off control for said plurality ofhigh-frequency power amplifiers based on the power control signal toadjust the average power of the output signal of said power amplifier.15. A radio wave transmitter comprising the power amplifier according toclaim 8, characterized by further comprising: a digital baseband circuitfor generating the power control signal, an I-signal, and a Q-signal;and a polar coordinate conversion circuit for generating the envelopesignal and the carrier signal based on the I-signal and the Q-signaldelivered from said digital baseband circuit, wherein said AD converterreceives the envelope signal delivered from said polar coordinateconversion circuit, a high-frequency power amplifier at a first stageamong said plurality of high-frequency power amplifiers receives thecarrier signal delivered from said polar coordinate conversion circuit,and said power controller receives the power control signal deliveredfrom said digital baseband circuit, and conducts switching control forsaid high frequency switches based on the power control signal to adjustthe average power of the output signal of said power amplifier.
 16. Thepower amplifier according to claim 3, wherein said envelope signalapplied to said AD converter has a substantially constant average power.17. The power amplifier according to claim 4, wherein said envelopesignal applied to said AD converter has a substantially constant averagepower.
 18. The power amplifier according to claim 3, wherein saidcarrier signal is a signal which includes only a phase modulatedcomponent of the high-frequency modulated signal.
 19. The poweramplifier according to claim 4, wherein said carrier signal is a signalwhich includes only a phase modulated component of the high-frequencymodulated signal.
 20. The power amplifier according to claim 5, whereinsaid carrier signal is a signal which includes only a phase modulatedcomponent of the high-frequency modulated signal.